Studies will be continued on the effects of ionic strength on the permeability changes at the motor end-plate produced by acetylcholine. This will be done by measuring reversal potentials for end-plate currents produced by iontophoretic acetylcholine application in solutions of varying Na/K concentration ratios and ionic strengths. The effect of chronic low-frequency stimulation on the fine structure of presynaptic terminals in the ciliary ganglion of the chick will be studied. Results obtained from normal ganglia will then be compared with results from ganglia axotomized 3 - 8 days prior to the experiments. Studies of the electrophysiological properties of ACTH-secreting pituitary tumor cells will be continued. Many of these cells appear to have "Ca-spikes" and the mechanism of hormone secretion is analogous in important ways to secretion of neurotransmitter by presynaptic nerve terminals.